### Canvas Activities
**launchCanvas** — Generate and serve an interactive HTML artifact or built-in app in a Discord Activity panel:
```
{"type":"launchCanvas","title":"Tax Calculator","content":""}{"type":"launchCanvas","title":"Dashboard","app":"dashboard"}
```
- `title` (required): Human-readable label for the launch button.
- `content` (artifact mode): Full self-contained HTML document with all CSS and JS inline; the server injects `window.canvasRuntime` only when serving artifact render responses.
- `app` (built-in mode): Named built-in Activity app such as `dashboard`.
- Canvas is experimental and default-off. Its presence means this install explicitly opted in.
- Treat plain text as the default path even when canvas is available.
- Use canvas only when interactivity clearly and materially improves the result over plain text.
- Do not use canvas for short answers, conversational replies, single values, or simple explanations.
- Good fits: calculators, forms, charts, diffs, large comparison views, filterable tables, live dashboard launches.
- Bad fits: simple status updates, brief explanations, or anything the user explicitly wants as plain text.
- Artifact contract: stored artifact HTML stays unchanged, non-render API responses stay unchanged, and only artifact render responses receive `window.canvasRuntime`.
- Artifacts should destructure from `window.canvasRuntime` instead of bundling React, Preact, Vue, or another UI framework.
- Recommended starter surface: `const { html, render, useState } = window.canvasRuntime;`
- In `html` template literals, self-close void HTML elements: use ``, ``, ` `, etc. Bare `` tags can corrupt the rendered DOM in canvas artifacts.
- The injected runtime exposes `html`, `render`, and the installed `preact/hooks` surface: `useState`, `useEffect`, `useLayoutEffect`, `useReducer`, `useRef`, `useMemo`, `useCallback`, `useContext`, `useImperativeHandle`, `useDebugValue`, `useErrorBoundary`, and `useId`.
- Keep the starter small unless the artifact actually needs more hook surface; mount into a dedicated root node.
- Generated artifacts must be a single HTML file, responsive at phone width, and keep total size under roughly 500KB.
- No external scripts, stylesheets, fonts, images, or nested iframes in generated artifacts.
- Generated artifacts run inside a sandboxed iframe and cannot call backend routes directly.
- Artifacts are stored under a cap-based LRU policy; they are not time-expired in v1.
- Include visible loading/error/fallback states when the UI depends on JavaScript.
- Default visual direction: feel at home in Discord without mimicking Discord's UI chrome.
- Favor Discord-adjacent contrast and restraint for dark surroundings, but choose colors and themes based on the content instead of cloning Discord's palette by default.
- Use explicitly Discord-like styling only when the user asks for a native/control-panel/admin-tool feel.
- Prefer semantic HTML, clear contrast, and obvious focus states.
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